The myoepithelial cells that make up the proventriculus of the polychaete worm Syllis spongiphila undergo regenerative calcium spikes. Mn ions pass through the calcium channels and also support regenerative events. Spikes elicited in Mn-containing solutions are of longer duration than those elicited in Ca-containing, Mn-free solutions. It is possible that Ca ions may play a role in the process of repolarization and that Mn ions compete with Ca ions. The effects of Ni ions, Co ions and Fe ions on the durations of Ca-spikes and Mn-spikes will be studied. Tests will be conducted to determine if repolarizations has a threshold and if it is a result of increased conductance to K ion or to Cl- or of only decreased conductance to Ca ions. The fate of calcium within the myoepithelial cells will be studied by bathing the preparations in solutions containing 45Ca, stimulating them to elicit Ca-influx, and then preparing the tissues for light microscopic autoradiography. The myoepithelial cells consist of only 1 or 2 sarcomeres which reach 40 micrometers in length. Thus, in isolation, these cells offer the opportunity to study single, unusually large, functional units of striated muscle. Techniques and conditions required for electrophysiological study of isolated cells will be investigated. Characteristics of isolated cells will be compared with known characteristics of cells in the intact proventriculus.